On a 2004, Subaru, WRX 2.0, sometimes the idle will only be about 500, but normally it runs about 1,000. It's random. It hasn't done it for about a month, and now is starting to do it again.

Any, thoughts, ideas, or suggestions on what would cause that to happen?

Stab in the dark here but ohm out the throttle position switch per the manual. You could clean the MAF sensor and check your exhaust to see if it has any back pressure or is restrictive.

MAF sensor has been cleaned with MAF sensor cleaner, but will try and figure out exactly where this throttle position switch is located on the throttle body, and what the ohm is.

At the moment, it is back to running normal again.